Magnetic focusing device



Dec. 12,1950 J, P, UAM 2,533,687

MAGNETIC FOCUSING DEVICE Filed May 27, 1949 n m u In I v u Ill I l IN V EN TOR.

@iizmesfi 0mm, BY

Patented Dec. 12, 1950 James P. Qu am, Chicago, Ill., assignor to Quam- Nichols Company, Chicago, 111., a corporation of Illinois Application May 27, 1949, Serial No. 95,731

4 Claims. (01. 250-161) This invention relates generally to apparatus for focussing an electron beam such as the beam of a cathode ray tube, and more particularly to a permanent magnet device of this type'inwhich the focussing effect can be adjusted.

In many applications, it is desired to focus a beam of electrons on a particular surface such as on the screen of a cathode ray tube in atelevision receiver. The focussing device acts'on the electron beam in generally the same manner that an optical lens acts on a beam of light rays to cause the beam to converge on a given point or surface. For focussing a beam of electrons, a magnetic field is required in which the lines of flux are parallel to the electron beam. In the prior art, such iocussing fields have been produced by electromagnetic coils or solenoids positioned about the beam of electrons. In such devices the current in the coil can be controlled to adjust the field so that the beam is focussed at the desired points.

It has been proposed to use permanent magnet structures for focussing an electron beam. In these structures it is necessary that some means of adjustment be provided to accurately control the field about the electron beam. This may be accomplished by the use of a coil in addition to the permanent magnet with the current of the coil being controlled. Such a structure, however, greatly increases the cost of the unit and is therefore undesirable. It has also been proposedto adjust the air gap of the permanent magnet structure to thereby adjust the strength ofthe field. While such an arrangement i effective to change the strength of the field, the change in the width of the air gap and the re' sulting change in the position of the air gap on the tube are objectionable as these factors also afiect the focussing and should preferably be fixed at optimum values.

It is, therefore, an object of the present invention to provide an improved permanent magnet device for focussing the beam of a cathode ray tube, in which the strength of the magnetic field can be adjusted without changing the width or position of the air gap. Y

A further object of this invention is to provide an adjustable permanent magnet focussing device for a cathode ray tube which provides a uniform field of optimum strength about the neck of the tube for focussing the electron beam therein.

A feature of thi invention is the provision of a focussing device for a cathode ray tube having magnetic plates with openings therein to receive the neck of the cathode ray tube and defining an air gap about the neck of the tube, with a plurality of permanent magnets between the plates for producing a field at the air gap, and an adjustable crew for shunting the field and thereby varying the strength or the field at the air gap.

the accompanying drawings in which:

Fig. 1 illustrates the focussing device in accordance with the invention in an operative position on a cathode ray tube;

Fig. 2 is a front view of the focussing structure;' and Fig. 3 is a side view of the focussing struc ture.

In practicing the invention, there is provided a magnetic structure including a pair of pole ieces made of material having low reluctance with the pole pieces having openings therein and inturned rims. magnets are positioned between the pole plates and are firmly secured thereto to provide a rigid overall structure. The inturned rims of the pole pieces provide an air gap across which a magnetic field is produced by the magnets. A screw isthreaded in one of the pole pieces and is adjustably positioned with respect to the other pole piece to provide a shunting field between the pole pieces. Adjustment of the shunting screw therefore controls the strength of the field-at the air gap. The permanent magnets and the shunting screw are all positioned at the edge of the pole pieces remote from the air gap so that the pole pieces. are effective in equalizing the fields of the magnets and provide a uniform field distribution about the air gap.

In Fig. 1, there is illustrated a cathode ra tube in having a neck portion H', and a front face l2 on which may be provided a fluorescent surface I3. The front face l2 and the neck ll may be joined by flared intermediate portion in the usual way. The tube may include a base l4 through which connection is made to the elements within the tube. A socket I5 is shown coupled to the base I 4 for making connections to the elements in the tube.

The permanent magnet focus device is indi-' cated generally at 20 and includes pole pieces 2| and 22 having openings 23 therein for receiving the neck I I of the cathode ray tube. I The two pole pieces may be of identical construction. Inturned rims 24 and 25 are provided on the pole pieces and form an air gap 25 therebetween. These annular rims may have restricted or bevelled pole faces 32 which restrict the field and thereby improve the operation of the iocussing device. More specifically, a pole face 32 is bevelled, sloped, or slanted inwardly as shown A plurality of permanent Figs. 1 and 3, to restriotor concentrate the field adjacent the tube neelr and hence the. seam therein. A magnetic field is provided in the air gap by a plurality of magnets 21 spaced about the periphery of the pole pieces 2| ann n. The strength of the field in the air gap can be adjusted by the shunting screw 28 which-isillus trated as threaded in polepiece"'2-2i A. second air gap is provided between the end 29 of the screw 28 and the pole piece 2| wnionreanbe-var 'ing beam 'o'f'ele'ctrons including a heater 35; a

cathode 35, and grids 3 1 and =38. These gridsma lie-of a' c'onflgurationto 'cause oeneeeen of the 'b'ea'm so that the ions are removed fromtlie electron stream in a wellknown manner. beam of electrons is directed through anop'en ing 3'19 in-the grid "38 and after passing through the-opening t!) the stream will tend to diverse asindicated at 4H3 It'is obvious thatsuch a di verging beam would produce a large spotcntli'e s'crcen'an'd this would'no't besatis'facto'ry in most instances'as-ina television receiver as it would result in blurring of the picture. The iocus'sing device 2o therefore provides a field in "the air -gap 26 which acts on the diverging stream of"elec tronswanucauses thestreamto converge as indicated at 4|. split cause's tnebeam to beconcentrated so that action-inf the focu's'sing devicedepends "upon the strength cftlie field in the air gap 25-and there-' fore the focussing can be controlled "by the shunting screw za'w'ni'cn controls the "field in the previouslystated the new in the airgap 2 s is produced by thema'gnets 21' which are provid'ed between the pole ieces 2| and 2'2 and wnich are' spaced fromthe air gap 25. Theip'ole pieces and 22'are ma'd'e of material'having low reluctance so thatthe'field in theair gap Willno't be" concentrated adjacent the magnets butwill be subs tantially uniform throughout'the entire air'igapzfi. The rims and 25 permitspacing the DolDieces at a distance greater than the desired air gap so that longerrnagnets can be usedto'provide the magneti'c'field needed, and

the stray news between. the pole 'piecesare reduced. The strength oftne field in the air gap was adjustable by the sl'iuntihg'scl e'w zcwnn tli'e'fiuxin the air gap beingvery small when the end29 ofthe's'cre'w 28isadjac'ent the pole piece 2| enca maximumwnen theend' 293s at 'o'r near The shunting screw: can be. easily made to provide variations "of "plus or:

the ore piece 22.

may include lu s '30 for supporting "the same on abracket as indicated at 3-1 which may be secured to the receiver cabinetor the receiver chassis. -An insulating 'controll rod' 4 5 may besecured to the shunting screw: 28" for adjusting the position on, tneserew bva knob time rear The reduction in the size of the vide the field strength necessary d imensions -of' tl'i'e"focussing structure are relativelivcriticall "The following gives the values found most" desirable for use in television receiversi usingcathode ray tubes from 10 to 12 inches in diameter:

Pole pieces 2| and 22:

putside diameter, 3%"? Material--colii' rclled' steel}.

Air gap ZGbetWeen'pole pieces, 3 Shuntingscrewcold rolled steel; Perrnanent magnets--Alnico #5,. 1 diameter;

It-i'sPobv-ious that certain of: these di'rnensions are interrelated. For: example; tnexdiameterenu thickness of thewpole 'pieces are related andzii' a larger' diaineter is used', the: fieid might be uni formlydistrib'uted about' the air gap -by poles on less thickness (higher reluctance'i-i iiisoit less than three magnets are the pole pieces" would to larger a." thicker to properl distribute the-held; ei-heroes it more magnets are used tne siz'e or thenon: pieces could .prbbablY- reduced.-

For use with a 10" cathode ray tubeenen on the order oi -600 gauss "is-'requii ed for or the properroous; To provide the r" uire an jc'stm'ent;the magnetic-structure niay m netized- -to =provide' a fieltl 'at 'the stinger- 6f about 700 'gausa- 'I his field can "then be rdil'c'ed ad iusnriesorew'to-aslawns-redeemasonviousl y provide adequateadiiistment qo opti mum-rows; afir g'ap'of i% "was"found-=to be fields between the pol'e piec'es arenot oujeonom able.

The perina nent magnet structure described lia'sben Tohnd tb be very satisfactory The adjusting screw 'provides tlie variations 'iir field strength required and dies not distbrt t-he field. The use of three permanent magnets spaced about the pole" pieces provi'iiesbdtlia' mgfiisr satisfactory magnetic held" and Very" rugged construction. The" thl'e ii'l'a g l'ie't's" pro"- in; a "minimum space and with a small amoun f permanent magnet f rn'aterial. The distribut nof'therncignets' inthls waynrovides a v'eiyuiiiforin fielfl iii nicii raciiitates oonnection" of the neareriets and poie pieces to provide a rugged overall structure? polepieces can be punched from sheet? in with-the beveled edges; toprovidethc rest pole faces; being. machined 'onn screwmachine: The "magnets'andjpole pieceshiay b'e "se'cured 'tc ge'ther byinimersionin a sol'der bath or in a y other suitable way, 'Iliecomplete" focussing' aevice is smaller" and lighter then available" -'i'ei:= 1 tromagn'eticfocussingjdevice's. v Permanent magnet "focussing '-in ac cordance with the invention are much ie'ss tifi pensive than electromagnet or combined permanent and electromagnet devices. In the first place, the focussing structure itself is less expenslve than an equivalent coil. Also, no rheostat or other auxiliary control is necessary for controlling the focussing device. Further, no outside energy is required so that the rectifier in the television receiver or other device in which the device is used need not provide energy for the focussing device. These various factors contribute to make a large overall saving in cost.

While one embodiment of the focussing device in accordance with the invention has been illustrated, it is obvious that various changes and modifications can be made therein without departing from the intended scope of the invention as defined in the appended claims.

I claim:

1. A magnetic structure for focussing a beam of electrons including in combination, a pair of pole pieces, said pole pieces each having a body portion with a beam receiving opening therein, and with said body portions being spaced apart from one another, permanent magnet means extending between said body portions of said pole pieces, said pole pieces each having a part on the inward side thereof at said opening, said parts providing an air gap therebetween having a substantially constant length less than half the spacing between said body portions of said pole pieces, at least one of said parts on said inward side having a bevelled annular edge as a pole face for providing a concentrated field in said air gap, and adjustable means on one of said pole pieces for providing a shunt magnetic path between said pole pieces to adiust the strength of the magnetic field in said annular air gap, said permanent magnet means and said adjustable means being magnetically coupled to said pole pieces and being radially spaced from said body portion openings so that the magnetic field is distributed through said pole pieces and the field in said annular air gap is substantially uniform.

2. A magnetic structure for focussing a beam of electrons including in combination, a pair of pole pieces, said pole pieces each having a body portion with a beam receiving opening therein, and with said body portions being spaced apart from one another, permanent magnet means extending between said body portions of said pole pieces, means for holding said pole pieces and said magnet means in assembled relation, said pole pieces each having a part on the inward side thereof at said opening, said parts providing an air gap therebetween having a substantially constant length of the order of one-third the spacing between said body portions of said pole pieces, at least one of said parts on said inward side having a bevelled annular edge as a pole face for providing a concentrated field in said air gap, and adjustable means on one of said pole pieces for providing a magnetic path between said pole pieces to adjust the strength of the magnetic field in said annular air gap, said permanent magnet means and said adjustable means being magnetically coupled to said pole pieces.

3. A magnetic structure for focussing a beam of electrons including in combination, a pair of pole pieces each having a body portion with a beam receiving opening therein, and with said body portions being spaced apart from one another, permanent magnet means extending between said body portions of said pole pieces, at

least one of said pole pieces having a part on the inward side thereof at said opening which forms an air gap with the other one of said pole pieces having a substantially constant length of less than half the spacing between said body portions of said pole pieces, said part on said inward side having a bevelled annular edge as a pole face sloping inwardly toward the beam receiving opening of said one pole piece for provid ing a concentrated fiield in said air gap, and adjustable means on one of said pole pieces for providing a shunt magnetic path between said pole pieces to adjust the strength of the magnetic field in said annular air gap, said permanent magnet means and said adjustable means being magnetically coupled to said pole pieces and being radially spaced from said body portion openings so that the magnetic field is distributed through said pole pieces and the field in said air gap is substantially uniform.

4. A magnetic structure for focussing a beam of electrons including in combination, a pair of pole pieces each having a body portion with a beam receiving opening therein, and with said body portions being spaced apart from one an" other, permanent magnet means extending between said body portions of said pole pieces, said pole pieces each having a part on the inward side thereof at said opening, said parts providing an air gap therebetween having a substantially constant length which is substantially less than the spacing between said body portions of said pole pieces, said parts on said inward side of said pole pieces each having a bevelled annular edge as a pole face for providing a concentrated field in said air gap, and adjustable means on one of said pole pieces for providing a magnetic path between said pole pieces to adjust the strength of the magnetic field in said annular air gap, said permanent magnet means and said adjustable means being magnetically coupled to said pole pieces.

JAMES P. QUAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Num er Name Date ,1 ,421 Kuehni Dec. 14, 1937 2,200,039 Nicoll May 7, 1940 2,212,206 Holst et al Aug. 20, 1940 2219,193 Mynall Oct. 22, 1940 2,224,933 Schlesinger Dec. 17, 1940 2,234,720 De Tar Mar. 11, 1941 2,305,761 Borries et a1. Dec. 22, 1942 2,336,837 Bedford Dec. 14, 1943 2,416,687 Fry Mar. 4, 1947 2,418,487 Sproul Apr. 8, 1947 2,431,077 Pooh Nov. 18, 1947 2,433,682 Bradley Dec. 30, 1947 2,440,403 Jackson Apr. 27, 1948 2,442,975 Grundrnan a- June 8, 1948 2,443,973 Asling June 22, 1948 2,456,399 Gethmann Dec. 14, 1948 2,494,459 Torsch Jan. 10, 1950 FOREIGN PATENTS Number Country Date 472,165 Great Britain Sept. 13, 1937 521,439 Great Britain May 22, 1940 597,255 Great Britain Jan. 21, 1948 615,553 Great Britain Jan. 7, 1949 848,180 France July 17, 1939 871,483 France Apr. 27, 1942 

